The designs of compact fluorescent lamps have as their principle aim the obtainment of significant energy savings over the use of incandescent lamps while attaining a comparable level of light output. It is also a significant advantage that such compact fluorescent lamps have a considerably longer life than a conventional incandescent lamp.
With most of such fluorescent or low pressure discharge lamp devices, it is necessary to provide a ballasting circuit to perform the function of conditioning the current signal used to drive the discharge lamp. An example of a compact fluorescent lamp utilizing a typical ballasting circuit can be found in U.S. Pat. No. 4,481,442 issued on Nov. 6, 1984, to Wolfgang Albrecht et al. It will be noted that the compact fluorescent lamp described in this patent consists of a bent discharge envelope which contains mercury gas. Furthermore, it will be noted that the ballasting circuit described in this patent relies on an electromagnetic type of ballasting; that is, one that requires the use of a magnetic core transformer to condition the current signal. Because such a ballasting arrangement operates at a power line current frequency of 60 hz which can result in lamp flicker, it has been determined that an electronic high frequency ballast that would eliminate the occurrence of lamp flicker or light variation, would be preferable. An example of a high frequency electronic ballast arrangement for a gas discharge lamp can be found in U.S. patent application Ser. No. 08/020,275 filed on Feb. 18, 1993, by Louis R. Nerone, now U.S. Pat. No. 5,341,068, issued Aug. 23, 1994.
It will be noted that the ballast arrangement is typically housed in a base member, and that such base member can have an upper cap portion which surrounds pinched seals of the outer ends of the tubular discharge envelope. Though this arrangement has proven to be simple and reliable when used with lower frequency circuits, it may be necessary to utilize additional housing/lamp envelope configurations when a high frequency electronic ballast circuit is utilized. For instance, with the higher frequency electronic ballast arrangement, dynamic losses can potentially occur wherein the term "dynamic losses" can be considered as that amount of energy in the circuit that is not converted to light by way of the energization of the lamp but is otherwise lost in the form of heat dissipated. Therefore, in order to prevent a thermal runaway condition or a condition where the discharge envelope operates at a higher temperature than would be intended it would be advantageous if operating temperature conditions could be managed so as to avoid damage to the lamp or lamp base. One way to avoid overheating conditions would be to increase the efficiency of the ballast circuit so as to insure the maximum conversion of input energy to light output. Such a high efficiency ballast circuit could be designed to operate with the lamp and base configuration of the typical compact fluorescent lamp, however, the increased cost and complexity could make such a lamp commercially undesirable. Alternatively, a heat sink arrangement may be developed which channels heat to a location where it could be more readily dissipated. With this alternative however, it must be understood that the housing base is constructed of a molded plastic material that could not accommodate dissipation of a significant amount of heat and moreover, must be adaptable to both a base-up and a base-down orientation in a light fixture thereby further complicating any type of heat sinking arrangement in the housing base.
It has been observed that the occurrence of an excessive heat condition in the lamp ballast and base housing configuration will occur only in the most extreme circumstances (i.e. excessively high line voltage) and/or under conditions which can be best described as misuse (i.e. improperly ventilated fixtures). Therefore, another alternative to adding components and therefore cost to the overall product, given the small likelihood of an excessive heat condition occurring, would be the provision of a controlled failure attribute. It would therefore be desirable to provide a mechanism that in the event of the occurrence of thermal conditions beyond a predetermined level, a controlled lamp failure would occur.
In addition, upon an unlikely excessive thermal condition occurring, the base member and/or lamp envelope could have potentially been damaged. However, as a result of the controlled failure the base housing member would be left undamaged, and upon the occurrence of significant lamp envelope violation in the controlled region, the fill could be substantially contained within the base member. It would therefore be desirable to maintain the envelope fill in the base member upon the occurrence of thermal conditions beyond a predetermined level.
Accordingly, it is an object of the present invention to provide a pinch seal region employing a conditioned glass envelope end to efficiently shut down the lamp prior to an excessively high temperature condition.
It is a further object of the present invention to provide an environmentally beneficial discharge lamp designed to maintain the envelope fill materials in the base member upon shut down.